Process for separation of dissolved hydrogen from water by use of palladium and process for coating palladium with palladium black

ABSTRACT

Dissolved gaseous hydrogen in water is separated from the water by placing the water in contact with a thin metallic film of palladium or palladium-silver alloy, both sides of which film have been coated with palladium black. The other side of the film has less pressure than the partial pressure of the hydrogen dissolved in the water. The hydrogen dissolved in the water permeates the film and passes to the other side of it. Preferably the palladium black is applied to the metallic film by etching the film, rubbing palladium chloride powder on the film, reducing the palladium chloride to palladium black by exposing it to gaseous hydrogen, depositing additional palladium black from a palladium chloride solution and rubbing the palladium black coating to remove excess black and provide a tightly bonded adherent coating.

United States Patent [15.] 3,678,654 Low et al. July 25, 1972 1 PROCESSO SEPARATION OF 3.350326 1 111967 Markrides et al ..55/l6 DISSOLVEDHYDROGEN FROM WATER BY USE OF PALLADIUM AND PROCESS FOR COATINGPALLADIUM WITH PALLADIUM BLACK Primary Examiner-Charles N. HartAttorney-Russell E. Schlorff, Marvin F. Matthews and John R. Manning [57] ABSTRACT [72] lnventors: George M. Low, Deputy Administrator of theNational Aeronautics and Space Adi s s aq in z ii zgf gg waer ypacmgewaermconacwi a inme icim zp a:g gr F 2 22352 of palladium orpalladium-silver alloy, both sides of which film Dlive Granada; Hills91344 y have been coated with palladium black. The other sideof the filmhas less pressure than the partial pressure of the hydrogen [22] Filed:July l 7, 1970 dissolved in the water. The hydrogen dissolved in thewater permeates the film and passes to the other side of it. [2]] ApplPreferably the palladium black is applied to the metallic film byetching the film, rubbing palladium chloride powder on the film,reducing the palladium chloride to palladium black by (gill exposing itto gaseous hydrogen depositing additional palladi 58 d l 6 l 5 um blackfrom a palladium chloride solution and rubbing the 1 le 0 are 8,palladium black i g to remove excess black and provide a tightly bondedadherent coating. [56] References Cited 8 Claim, 4 Drawing FiguresUNITED STATES PATENTS .2 V .7

3,232,026 2/1966 McKinley ...55 l6 Patented July 25, 1972 3,678,654

2 Sheets-Sheet l I so L I (bar/e: E /4/6/'/yfi/ INVENTOR.

ATTORNEY Patented July 25, 1972 2 Sheets-Sheet 2 INVENTORv ATTORNEYPROCESS FOR SEPARATION OF DISSOLVED HYDROGEN FROM WATER BY USE OFPALLADIUM AND PROCESS FOR COATING PALLADIUM WITH PALLADIUM BLACK ORIGINOF THE INVENTION The invention described herein was made in theperformance of work under a NASA Contract and is subject to theprovisions of Section 305 of the National Aeronautics and Space Act of1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).

BACKGROUND OF THE INVENTION Applicant does not know of any previous artfor the separation of dissolved hydrogen from water by having thehydrogen permeate a palladium film. The closest field of which applicantis aware is the separation of hydrogen from a gaseous stream by havingthe stream contact a palladium film with the hydrogen component of thestream permeating that film. The other aspect of the present developmentis in the field of forming a palladium black coatlng on a palladiumfilm, especially for aiding the permeation of that film by hydrogen.

US. Pat. No. 3,232,026 issued Feb. 1, 1966 for Separation Method UsingActivated Diffusion Barriers upon the application of David L. McKinleyteaches the separation of a hydrogen component from a gaseous mixture byplacing that mixture in contact with a thin metallic palladium filmwhich has been coated on each side with palladium black. Palladium ispermeated by hydrogen and the coating of both sides of the palladiumfilm with palladium black greatly enhances the rate of permeation andhence separation of hydrogen from the gaseous mixture, especially attemperatures in excess of 200 C. U.S. Pat. No. 3,232,026 also refers tocertain techniques for applying palladium black.

Neither US. Pat. No. 3,232,026 nor any other prior art of whichapplicant has knowledge, teaches the separation of dissolved hydrogenfrom water by the use of a palladium film coated on each side withpalladium black nor the process for coating palladium with palladiumblack that is described and claimed herein.

SUMMARY OF THE INVENTION The Apollo spacecraft carry fuel cells whichproduce water saturated with hydrogen at operating conditions-usuallyabout 60 p.s.i.a. and 160 F. This fuel cell water constitutes a potablewater supply for the astronauts and has other uses. The dissolvedhydrogen in this water causes problems, especially at zero gravity andlow pressures. Reduction of the hydrostatic pressure on the effluentwater from the fuel cell causes the dissolved hydrogen to revert to thegaseous phase which can occupy a considerable volume, depending upon thefinal pressure. Accumulation of hydrogen during a mission can seriouslyreduce the storage capacity of the potable water tank. If concentratedin localized areas, the hydrogen constitutes a potential fire andexplosion hazard. In addition, a hydrogen water emulsion is a source ofirritation to the astronauts during drinking or reconstitution offreeze-dried foods.

It is therefore a general purpose of the present invention to provide aprocess for the removal of dissolved hydrogen from water, especially atambient temperatures.

In separating the dissolved hydrogen, use is made of thin palladium orpalladium-silver alloy film, coated on each side with palladium black.Preferably for structural strength, the film is in the form of a tube.Previous methods known to Applicant for applying palladium black topalladium film are not satisfactory for coating the interior ofrelatively small tubes, such as Math inch O.D. tubing or are too timeconsuming.

it is therefore another object of the present invention to provide aprocess for applying a coating or layer of palladium black to apalladium or palladium-silver alloy film especially for use inaccelerating the permeation of the film by hydrogen.

In the prior art, there is a process, hereinafter usually called the wetprocess," for applying palladium black to a film of palladium orpalladium-silver alloy in which a film is exposed to hydrogen so thatthe palladium absorbs hydrogen. A solution is made of palladium chloridein hydrochloric acid, the acid being used because of the difficulty ofdissolving palladium chloride. The hydrogen-containing film is broughtin contact with the palladium chloride solution so that the hydrogen inthe palladium film reduces the palladium chloride to palladium black.

One of the difiiculties with the wet process is that it takes aconsiderable period of time, usually several days, for the uncoated filmto absorb the maximum amount of hydrogen that it can hold. This hydrogenis necessary for the reduction of the palladium chloride.

It is therefore another object of the present invention to provide amethod of increasing the rate at which a palladium or palladium alloyfilm will absorb hydrogen prior to depositing a layer of palladium blackby the wet process.

Other and further objects, features and advantages will be apparent fromthe following description and presently preferred examples of thepresent invention, given for the purpose Of disclosure and taken inconjunction with the accompanying drawings.

The process for separation of the dissolved gaseous hydrogen from wateris based on the discovery that if a metallic film made from palladium ora palladium-silver alloy is coated on each side with palladium black,one side of the film is provided with less pressure than the partialpressure of the hydrogen in the water, and the other side of the film iscontacted with the water containing the dissolved hydrogen, thatthedissolved hydrogen will leave the water andpass through the film evenat ambient temperatures. Any of the palladiumsilver alloys commonly usedfor separation of gaseous hydrogen from a mixed gas stream may be usedsuch as percent palladium and 25 percent silver. PreferAbly the film isa tube having an approximate one-eighth inch outside diameter.

With respect to the coating of palladium black, the present invention isbased upon the discovery that an excellent coating can be applied topalladium or palladium-silver alloy film by etching the film, rubbingpalladium chloride powder on the etched film, and reducing the palladiumchloride to a palladium black coating by exposing the palladium chlorideon the metallic film to gaseous hydrogen. If a second coating is not tobe applied by the wet process, the coating formed from the powder ispreferably burnished or rubbed after formation as this appears to make abetter contact of the coating with the film and thereby increases therate of permeation of hydrogen.

While the palladium black coating formed from the palladium chloridepowder may be used alone, a better product may be obtained by exposingthe film coated with the initial coating of palladium black to the wetprocess to deposit an additional palladium black coating by thereduction of the palladiurn chloride in the solution with the use of thehydrogen contained in the film coated with the initial palladium blackcoat ing. After carrying out the wet process, the final coating isburnished or rubbed. The entire time occupied in forming the initialcoat of palladium black is much less than the time necessary foruntreated film to become saturated with hydrogen.

Information available to applicant indicates that palladium blackapplied by the process of the present invention is superior in aidingpermeation by hydrogen to palladium black applied by any other methodknown to applicant.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partly schematicillustration of processing retort useful in applying palladium black inaccordance with the present invention.

FIG. 2 is an enlarged view, partly sectional, of a form of device usefulfor applying palladium chloride powder to the interior of palladiumtubes.

FIG. 3 is a view along the line 33 of FIG. 4.

FIG. 4 is a plan view illustrating one form of apparatus which may beused for separation of dissolved hydrogen from water.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings,there is illustrated in FIG. 1 a

glass processing retort for use in etching palladium tubes and reducingthe palladium chloride to palladium. The retort, indicated generally bythe numeral 10 has a glass cylindrical body 12 with a removable top 13.The body 12 contains a removable tube rack 14 upon which palladium tubes16 are placed and held in spaced relationship at their lower ends. Aperforated separator plate 18 near the upper end of the body 12 holdsthe upper ends of the tubes 16 in spaced relationship. Near the lowerend of the retort l and communicating with the interior of the body 12are a line 20 with a valve 22 for admitting air to the interior of thebOdy 12 and a line 28 with a valve 30 which serves as a drain from thebody 12.

Near the upper end of the body 12 are a line 38 with a valve 40 thereinfor admitting nitrogen to the interior of the body 12, a line 42 with avalve 44 for introduction of liquid into the body 12, a line 46 with apressure relief valve 48, a line 32 with a valve 34 for connection to avacuum source, and a line 47 with a valve 49 for introducing hydrogeninto the body 12. A pressure gauge 36 in the line 32 indicates thepressure within the body 12.

In FIG. 2 is illustrated a tool or device indicated generally by thenumeral 50 used for applying palladium chloride to the interior of thetubes 16. This tool 50 is made from a nylon rod 52 of which only one endis shown in FIG. 2. The rod has a first reduced diameter portion 54around which is placed a lint-free tissue paper 56. Between the firstreduced diameter portion 54 and the end 58 of the rod 52 is a secondreduced diameter portion 60 containing three O-rings 62 made ofneoprene. The diameters of the nylon rod 52, of the tissue paper 56 andof the O-rings 62 are such that these parts all fit the inside diameterof the palladium tubes 16.

An example of a preferred method of coating palladium orpalladium-silver alloy with palladium black is as follows. 20- inchtubes are cut from palladium-silver alloy tubes having 25 percentsilver. Each tube is Arth inch OD. and has a wall thickness of mil. Toclean the tubes, each is immersed in acetone, the acetone is drained,and the tubes are immersed in isopropyl alcohol with the inside diameterbeing flushed under slight pressure. All handling hereafter is withpolyethylene gloves.

The tubes are removed from the alcohol, drained, and blown dry. They areimmersed in a detergent and scrubbed. The interior is scrubbed with thedevice of FIG. 2. The detergent is flushed and the tubes thoroughlyrinsed in distilled water. The tubes are then inserted in a retortsimilar to that of FIG. 1.

Reagent-grade concentrated nitric acid is inserted into the retort 10until the upper ends of the tubes 16 are covered. The tubes are moved upand down frequently during a minute period to ensure fresh acid contactsthe tube interior and complete surface etching is obtained. The acid isdrained from the retort and the retort is filled again with concentratednitric acid with frequent agitation for about l5 minutes. The secondbatch of acid is drained off and the interior of the tubes and retort 10are rinsed with distilled water. The interior of the retort I0 is thenswept with nitrogen to remove liquid with final drying being undervacuum. Any remaining acid on the ends of the tubes where they are heldby the rack is removed with water and cotton swabs and the ends are thendipped in isopropyl alcohol and redried.

To applythe palladium chloride, one end of each tube 16 is dipped intopalladium chloride powder for about one-eighth to three-eighths inches.The tool of FIG. 2 is then inserted into the tube and moved back andforth to distribute the palladium chloride over the entire internaldiameter of the tube. This is repeated using the other end of the tube.This operation is repeated for a minimum of six times and then theexcess palladium chloride is blown from the interior of the tube. Thepalladium chloride powder is applied to the outside of the tubes byrubbing with a gloved thumb and forefinger. Here also, excess powder isremoved by blowing with nitrogen.

The tubes are then returned to the processing retort 10, a vacuum ispulled on the retort and then hydrogen is introduced into the retortuntil slightly above atmospheric pressure. After the hydrogen pressurestabilizes, the hydrogen atmosphere is maintained a minimum of 2 hoursand then it is swept out by nitrogen.

At this point, the palladium chloride is reduced to palladium blackinitial coating. To add another coat, a 0.3 percent solution ofpalladium chloride is hydrochloric acid is introduced into the interiorof the retort l0 and the tubes moved up and down in this solution withthe solution being drained and changed at 5 minute intervals. This soakin palladium chloride is maintained for about 30 minutes. The absorbedhydrogen within the palladium causes additional palladium black to bedeposited onto the initial coating. The palladium chloride solution isdrained and the tubes washed with distilled water. Thereafter, the tubesare dried using nitrogen and vacuum.

After the tubes are dry, air is introduced slowly into the retort 10.The air will react with hydrogen in the tubes 16 and cause them to heat.The internal temperature of the retort should not be allowed to exceed150 F. The tubes 16 can be cooled if necessary by evacuating the air andflowing nitrogen into the retort 10.

After the adsorbed hydrogen has been completely removed by the airoxidation step, the tubes are removed from the retort l0 and theiroutside surfaces burnished with lint-free tissue. The inside isburnished with a device identical to that of FIG. 2 except that it doesnot have the O-rings 60. It has also been found that ordinary pipecleaner material is satisfactory for the burnishing step.

Referring now to FIGS. 3 and 4, there is shown a hydrogen separatorindicated generally by the numeral 70 which may be used in the presentprocess of separating dissolved hydrogen from water. The hydrogenseparator 70 has a generally cylindrical base 72 open at its lower endand having a plate 74 at its upper end. Drilled through the plate 74 arefour rows 76, 78, and 82, respectively, of holes for receiving a seriesof tubes 16a, 16b and 160 made of palladium-silver alloy coated withpalladium black. Row 76 has three holes, row 78 has six holes, row 80has six holes and row 82 has three holes. Bored in the plate 74 underrow 76 is an inlet manifold 84 communicating with a line 85 connected toa source of water. This manifold 84 has an upstanding short section oftubing 86 extending through each of the holes in the row 76. Bored inthe plate 74 under the row 78 is a manifold 88 which has an upstandingshort section of tubing 90 extending through each of the holes in row78. Bored in the plate 14 under the row 80 is a manifold 92 which hascommunicating with it a short upstanding section of tubing 94 extendingupwardly through each of the holes in the row 80. Bored in the plate 74under the row 82 is an outlet manifold 96 connected to an exhaust line97. This outlet manifold 96 has communicating with it a short section ofupstanding tubing 98 extending upwardly through each of the holes in therow 96.

At each of the holes in the row 76, one end of a U-shapedpalladium-silver alloy tube 16a coated on the inside nd outside andpalladium black is attached by a threaded sleeve 100 to the shortsection of tubing 86 projecting upwardly from the manifold 84. The otherend of each tube 16a is secured by a sleeve 102 to an upstanding pieceof tubing 90 extending from one of the holes in the row 80. Similarly,three tubes 16b, identical to the tubes 16a, are connected between thesections of tubing 90 in the other three holes in row 78 and thesections of tubing 94 in three of the holes in row 80. Again, threetubes 16c identical to tubes are connected between the sections oftubing 94 in the other three holes of row 80 and the sections of tubing98 in the row 82.

These tubes 16a, 16b and 16c are additionally secured in position by aperforated teflon retainer plate 104 held in place by spacing bolts 106passing through sleeves 108, the teflon retainer plate 108 and the plate74.

Water containing dissolved hydrogen is introduced into the inletmanifold 84 and passes through the tubes 16a to the manifold 88. Waterentering the manifold 88 flows through the tubes 16b to the manifold 92.Water entering the manifold 92 flows through the tubes 16c into and outof the outlet manifold 96.

in operation of the device of FIGS. 3 and 4, the dissolved hydrogencontained within the water passing through the tubes permeates the wallsof those tubes. If desired, a bell jar may be placed over the tubes 16a,16b and 160 to rest upon the plate 74 and be evacuated to simulate outerspace.

An example of a preferred method of removing dissolved hydrogen fromwater is as follows. In a device such as is illustrated in FIGS. 3 and 4were placed tubes one-eighth inch in diameter, mil thick and made ofpalladium-silver alloy containing 25 percent silver coated withpalladium black having a loading of 2 mglcm Nine tubes, each 20 inchesin length, were arranged within the separator 70. Water at 75 F. with aflow of 10 cubic centimeters per minute and containing dissolvedhydrogen having a partial pressure of 60 p.s.i.a. was passed through theinlet manifold. The exteriors of the tubes were exposed to air whichremoved hydrogen from the palladium alloy tubes by oxidation. Thepartial pressure of the dissolved hydrogen dropped to 3.5 p.s.i.a.()peration of such a unit for over 5 months (3,700 hours) indicated noloss of efficiency in removal of hydrogen.

From the foregoing discussions, examples and description of theinvention, it is apparent that the objects set forth herein as well asothers have been achieved. Those skilled in the art will recognize thatthe principles of this invention may be applied in several ways, only afew of which have been exemplified herein specifically. Accordingly, theinvention is to be limited only by the spirit thereof and the scope ofthe appended claims.

What is claimed is:

l. A process for the separation of dissolved hydrogen from watercomprising:

a. providing a metallic film selected from the group consisting ofpalladium and palladium-silver alloy, both sides of said film beingcoated with palladium black,

b. providing on one side of the film less hydrogen pressure than thepartial pressure of the hydrogen in the water,

c. contacting the other side of the film with the water containingdissolved hydrogen at ambient temperature, and

d. passing the dissolved hydrogen through the film.

2. The method of claim 1 in which the film is tubular in shape.

3. The method of claim 1 in which the film is a tube having anapproximate one-eighth inch outside diameter.

4. A process for separating dissolve-d hydrogen from water,

' said process comprising:

a. providing a metallic film selected from the group consisting ofpalladium and palladium-silver alloy, both sides of said film beingcoated with palladium black formed by a process which includes (i)etching the metallic film, (ii) rubbing palladium chloride powder on theetched film and (iii) reducing the palladium chloride to palladium blackby exposing the palladium chloride powder on the metallic film togaseous hydrogen,

b. providing on one side of the film less hydrogen pressure than thepartial pressure of the hydrogen in the water,

c. contacting said other side of the film with the water, containingdissolved hydrogen, and

' d. passing the dissolved hydrogen through the film.

5. The process of claim 4 in which the metallic film is tubular inshape.

6. A process for separating dissolved hydrogen from water,

said process comprisin a. providing a metalfic film selected from thegroup consisting of palladium and palladium-silver alloy, both sides ofsaid film being coated with palladium black formed by a process whichincludes (i) etching the metallic film, (ii) rubbing palladium chloridepowder on the etched film, (iii) reducing the palladium chloride to apalladium black initial coating by exposing the palladium chloridepowder on the metallic film to gaseous hydrogen and (iv) depositing anadditional coating of palladium black by exposing the initial coating toa solution of palladium chloride whereby hydrogen in the film reducespalladium chloride in the solution to palladium black,

b. providing on one side of the film less hydrogen pressure than thepartial pressure of the hydrogen in the water, and

c. contacting said other side of the film with the water containingdissolved hydrogen, and

d. passing the dissolved hydrogen through the film.

7. The process of claim 6 in which the palladium chloride solutionincludes hydrochloric acid as a solvent.

8. The process of claim 6 in which the metallic film is tubular inshape.

2. The method of claim 1 in which the film is tubular in shape.
 3. Themethod of claim 1 in which the film is a tube having an approximateone-eighth inch outside diameter.
 4. A process for separating dissolvedhydrogen from water, said process comprising: a. providing a metallicfilm selected from the group consisting of palladium andpalladium-silver alloy, both sides of said film being coated withpalladium black formed by a process which includes (i) etching themetallic film, (ii) rubbing palladium chloride powder on the etched filmand (iii) reducing the palladium chloride to palladium black by exposingthe palladium chloride powder on the metallic film to gaseous hydrogen,b. providing on one side of the film less hydrogen pressure than thepartial pressure of the hydrogen in the water, c. contacting said otherside of the film with the water, containing dissolved hydrogen, and d.passing the dissolved hydrogen through the film.
 5. The process of claim4 in which the metallic film is tubular in shape.
 6. A process forseparating dissolved hydrogen from water, said process comprising: a.providing a metallic film selected from the group consisting ofpalladium and palladium-silver alloy, both sides of said film beingcoated with palladium black formed by a process which includes (i)etching the metallic film, (ii) rubbing palladium chloride powder on theetched film, (iii) reducing the palladium chloride to a palladium blackinitial coating by exposing the palladium chloride powder on themetallic film to gaseous hydrogen and (iv) depositing an additionalcoating of palladium black by exposing the initial coating to a solutionof palladium chloride whereby hydrogen in the film reduces palladiumchloride in the solution to palladium black, b. providing on one side ofthe film less hydrogen pressure than the partial pressure of thehydrogen in the water, and c. contacting said other side of the filmwith the water containing dissolved hydrogen, and d. passing thedissolved hydrogen through the film.
 7. The process of claim 6 in whichthe palladium chloride solution includes hydrochloric acid as a solvent.8. The process of claim 6 in which the metallic film is tubular inshape.